Bearings are devices that permit constrained relative motion between two parts. A plain bearing is the simplest type of bearing, comprising just a bearing surface and no rolling elements. Therefore the journal (i.e. the part of the shaft in contact with the bearing) slides over the bearing surface. The simplest example of a plain bearing is a shaft rotating in a hole. Two-piece plain bearings, known as full bearings in industrial machinery, are commonly used for larger diameters, such as crankshaft bearings. Self-lubricating plain bearings have a lubricant contained within the bearing walls. The lubricant is typically an integral element of the bearing material and remains part of the bearing's makeup for its entire life without the need for outside maintenance.
Plain bearings often contain a liner between the bearing surfaces to reduce friction. Typical prior art fabric liner systems used in self-lubricating bearings comprise a woven fabric combined with a resin binder to form a composite material that can be affixed to bearing surfaces. The fabric component of the composite consists of a top surface of lubricating yarns (typically PTFE), which degrade through motion at the working surface, providing the bearing with lubricant, and structural yarns (typically glass fibers), which help retain the lubricating yarns and provide the composite with its structural integrity.
Due to the temperature requirements stated in aerospace plain bearing specification AS81820 (the bearing is required to operate effectively from −55° C. to +163° C.), the selection of resin binders for composite liners systems has been generally limited to the phenol family. As a result, phenol-based resin binders have become an industry standard in prior art bearing technologies. However, there is a need for plain bearings that exhibit improved wear resistance and therefore increased working lifetime, in particular in high vibration applications.
The present invention seeks to tackle at least some of the problems associated with the prior art or at least to provide a commercially acceptable alternative solution thereto.